The last time I had a crown put on, it cost over $800, but let’s take that number for the calculation

Assuming my math is correct (see below), if I used two-thirds of a yard (.6) for each floss and flossed three times a day, every day, I could floss for over 15-and-a-half years before I had spent enough on floss to cover a crown.

Caveats: (1) This scenario is a bit simplistic because more may go into dental care than floss (e.g., tooth paste, tooth brushes, and mouth wash). (2) Floss does not necessarily prevent the kind of decay that brings the need for a crown. (3) I’m not a mathematician, so my calculations may be off.